Various mechanisms have been developed for use in meters to translate flow of a liquid, such as water, to a measurable quantity. One such mechanism known in the art is the use of a nutating ball and disc in a measurement chamber through which water flows under pressure. The measurement chamber is of known volume. As water passes through it, the ball and disc nutate. This nutation is then translated to rotation of a magnet, such that each rotation of the magnet represents a known quantity of water passing through the meter.
In a traditional nutating disc meter, such as that shown in FIG. 10, a measuring chamber is enclosed within a brass housing. The measuring chamber includes a ball socket that contains the ball of the ball and disc. A spindle extends radially from the top of the ball through an enlarged opening in the top of the ball socket. Above the ball is an inverted frustum, often called a control block. The spindle bears against the control block, which keeps the spindle offset from vertical, and thereby the ball and disc offset from horizontal. The angle of offset caused by the control block corresponds to the angle of the slope of the top and bottom walls of the measuring chamber. The ball and disc nutate in response to the flow of a pressurized liquid, such as water, through the measuring chamber. As the ball and disc nutate, the spindle precesses about the control block. The spindle contacts a tab on the end of a drive shaft, causing it to rotate. The drive shaft is coupled to a magnet and therefore each nutation of the ball and disc is translated to a rotation of the magnet. The magnet couples to a register on the outside of the meter housing, which contains mechanical, electrical, or electromechanical means of recording the number of rotations of the magnet and thereby measuring water flow through the meter.
The foregoing design suffers from several problems. First, the control block increases the height of the assembly, which necessitates a larger housing and thus more material to make the housing. This increases the cost of meter, because the housing is usually made of brass or other durable, weather-resistant material. Also, the spindle is usually made of stainless steel for its strength and anti-corrosive properties. The ball and disc, however, is made of plastic, and the spindle must be inserted precisely into the ball during manufacture. Thus, the prior art's use of a separate stainless steel spindle increases both the materials cost and the assembly cost of the meter. In addition, the ball socket must have a large opening in order for the spindle to precess about the control block. This in turn reduces the surface area of the ball socket available to distribute the load of the ball as it rotates, which results in increased wear of the ball socket over time.
The prior art design also requires multiple components for translation of motion and control. The offset angle of the ball and disc is controlled by the control block. Translation of nutation to rotation is accomplished with the spindle and drive shaft. Thus, three separate parts are necessary to perform these functions.
Thus, there exists a need for a meter in which a single element controls the angular offset of the ball and disc and translates nutation to rotation, and in which the requirement of a control block is eliminated to reduce the height of the meter and therefore the size of the meter housing, saving cost. Further, there exists a need for a nutating-disc meter in which the surface area of the ball socket is not compromised to accommodate a control block and a precessing spindle.